1. Field of the invention
The present invention relates to an improved heat generating resistor comprising a specific tantalum nitride containing TaN0.8 which excels not only in terms of heat generation performance but also in terms of durability upon repeated use and which can be produced at a reduced production cost. The heat generating resistor is applicable to various outputting mechanism-bearing devices or systems such as printers, facsimiles, copying machines, and composite mechanized retrieval systems, and also to their terminal printers of printing an object outputted on a printing medium. Particularly, the heat generating resistor is suitable for use particularly in a liquid jet system of discharging and flying printing liquid utilizing a thermal energy to thereby print an image on a medium such as ordinary paper, synthetic paper, fabric, or the like. The present invention includes an improved substrate provided with said heat generating resistor for a liquid jet head, a liquid jet head provided with said substrate, and a liquid jet apparatus provided with said liquid jet head. The present invention enables to produce any of said substrate, liquid jet head, and liquid jet apparatus respectively at an improved precision and at a reduced production cost.
2. Related Background Art
U.S. Pat. No. 3,242,006 (hereinafter referred to as Literature 1) discloses a tantalum nitride (TaN) film resistor (hereinafter referred to as TaN film resistor) formed by impressing a DC voltage of 5000 V between a cathode composed of Ta and an anode in a gaseous atmosphere comprising N2 gas and Ar gas under conditions of 400xc2x0 C. for the atmospheric temperature, 400xc2x0 C. for the substrate temperature, and 1xc3x9710xe2x88x924 mmHg for the partial pressure of the N2 gas to sputter the Ta cathode. Literature 1 describes that the TaN film is of a sodium chloride type structure rather than the anticipated hexagonal type structure. Further, Literature 1 describes production of Ta2N of hexagonal structure (hereinafter referred to as Ta2Nhex) and mixtures of the Ta2Nhex and TaN of a cubic structure. Hence, it is understood that Literature 1 discloses a resistor comprising a film composed of a tantalum nitride substantially comprised of TaN only (seemingly contaminated with foreign matters) (this tantalum nitride material will be occasionally called TaN single body in the following), a tantalum nitride material substantially comprised of Ta2N only (seemingly contaminated with foreign matters) (this tantalum nitride material will be occasionally called Ta2N single body in the following), or a tantalum nitride material comprised of a mixture of these.
Now, there are known a variety of printing systems of discharging and flying ink utilizing a thermal energy to form an ink droplet whereby printing an image on a printing medium. Of those printing systems, the so-called on-demand type ink jet printing system has been evaluated as being the most appropriate because the noise cased upon conducting printing can be reduced to a negligible order.
U.S. Pat. No. 4,849,774 (or German Patent No. 2843064) (hereinafter referred to as Literature 2) discloses a on-demand type bubble jet printing system which attains on-demand printing by causing film boiling for ink to discharge ink in the form of an ink droplet whereby printing an image on a printing medium. Literature 2 describes the use of a heat generating resistor composed of a metal boride (specifically, HfB2) or tantalum nitride. The tantalum nitride described in Literature 2 is apparent to include the TaN single body, Ta2Nhex single body, and mixtures of these described in Literature 1 in view of the priority dated of Literature 2 in relation to the publication date of Literature 1.
Now, it is understood that the heat generating resistor comprising HfB2 or tantalum nitride is compatible with the film-boiling phenomenon and satisfies the requirements relating to ink discharging characteristics, printing speed, and printing condition as far as the bubble jet printing system described in Literature 2 is concerned.
However, in on-demand type bubble jet printing systems provided with an markedly increased number of discharging outlets which have been developed in recent years after (specifically, after 1983) or will be developed in the future, it is commonly recognized that not the heat generating resistor composed of tantalum nitride but only a heat generating resistor composed of HfB2 or TaAl satisfies the conditions required for such markedly increased discharging outlets in terms of stability and durability.
Incidentally, there are a number of reports on thermal heads having a heat generating resistor composed of tantalum nitride in which the heat generating resistor is directly contacted with a heat-sensitive paper or an ink ribbon. The heat generating resistor herein is understood to be similar to that described in Literature 1.
Other than this, U.S. Pat. No. 4,737,709 (hereinafter referred to as Literature 3) discloses a thermal head having a heat generating resistor comprising a film of tantalum nitride (Ta2N) having a hexagonal close-packed lattice oriented in (101) direction which is formed by the reactive sputtering process. It is understood that Literature 3 is directed to an improvement in the thermal head in terms of the durability by using said specific tantalum nitride film as the heat generating resistor.
It should be noted to the fact that any of the tantalum nitrides films described in these documents has never been actually used as a heat generating resistor of an ink jet head, although they have been used in a thermal head.
Description will be made of the reason for this. That is, in the case of a thermal head, the electric power applied to the heat generating resistor is about 1 W for a period of 1 xcexcsec. On the other hand, in the case of an ink jet head, in order to conduct film-boiling of ink for a very short period of time, an electric power of a wattage in the range of from 3 W to 4 W is applied to the heat generating resistor, for instance, for a period of 7 xcexcsec. It is understood that the electric power applied to the heat generating resistor for such a short period of time in the case of the ink jet head is greater as much as several times the electric power applied to the heat generating resistor for a relatively longer period of time in the case of the thermal head.
In order to examine whether or not the foregoing conventional tantalum film resistors are practically usable as the heat generating resistor for an ink jet head, the present inventors prepared a plurality of ink jet heads each having a heat generating resistor composed of any of the foregoing conventional tantalum nitride films, and subjecting each of the ink jet heads to printing. As a result, there was obtained a finding in that there is a tendency for any of the heat generating resistors to be greatly varied in terms of the resistance value within a short period of time upon the application of a large quantity of an electric power thereto. Such variation in terms of the resistance value for the heat generation resistor is not serious in the case of a thermal head since it is not instantly influenced to an image obtained. However, in the case of an ink jet head, a serious problem entails in that generation of a bubble at ink is not stably occurred as desired to cause a decrease in the quantity of an ink droplet discharged, resulting in making an image printed to be inferior in terms in the quality.
Hence, the reason why any of the conventional tantalum nitride heat generating resistors described in the above documents has never been practically used in an ink jet head can be understood. In fact, there cannot be found any report in which the use of a tantalum nitride heat generating resistor in an ink jet head has been studied. And, in the ink jet heads in recent years, a heat generating resistor composed of HfB2 has been actually often used as their heat generating resistor.
Other than the above-described U.S. patent documents, there can be found U.S. Pat. No. 4,535,343 (hereinafter referred to as Literature 4), Japanese Unexamined-Patent Publication No. 59936/1979 (hereinafter referred to as Literature 5), and Japanese Unexamined Patent Publication No. 27281/1980 (hereinafter referred to as Literature 6) which disclose tantalum nitride films. Particularly, Literature 4 discloses a thermal ink jet printhead having a heat generating resistor layer comprising a tantalum nitride (Ta2N) film formed by means of the RF or DC diode sputtering process wherein a Ta-target is sputtered in an atmosphere comprising a gaseous mixture of Ar gas and N2 gas with a volumetric ratio of 10:1.
However, in an ink jet head provided with an markedly increased number of discharging outlets which have been developed in recent years, the heat generating resistor composed of tantalum nitride described in Literature 4 does not satisfy the conditions required for such markedly increased discharging outlets in terms of stability and durability for the same reason above described.
Literatures 5 and 6 disclose an ink jet recording head having a heat generating resistor composed of tantalum nitride (specifically, Ta2N single body) formed by the vacuum evaporation or sputtering process.
Any of the tantalum nitrides by which the heat generating resistors are constituted described in these Literatures 5 and 6 is one that has a so-called Ta2Nhexagonal structure (that is, Ta2Nhex). Any of these heat generating resistors composed of the Ta2Nhex single body is also problematic in that there is a tendency for the heat generating resistor to be greatly varied in terms of the resistance value to cause a decrease in the quantity of an ink droplet discharged, resulting in making an image printed to be inferior in terms in the quality, when recording is continuously conducted while discharging ink over a long period of time. Because of this, the Ta2Nhex single body is not practically usable as the constituent for a heat generating resistor in an ink jet head provided with an markedly increased number of discharging outlets for the same reason above described. In fact, there cannot be found any report in which the use of such Ta2Nhex single body as the heat generating resistor in an ink jet head has been discussed.
As above described, HfB2 has been evaluated as being suitable as the constituent of a heat generating resistor for use in an ink jet head since a heat generating resistor composed of HfB2 mostly meets the requirements for the heat generating resistor in an ink jet head, and the heat generating resistor composed of HfB2 has been often used in ink jet heads.
However, there is a fear for HfB2 as the constituent material of the heat generating resistor used in an ink jet head to be possibly in short supply. That is, only one or two companies are concerned with the production of HfB2 in the world. Therefore, stable supply of HfB2 is not always secured. In addition, Hf as the starting material in the production of HfB2 is a by-product obtained upon producing an atomic fuel. Thus, there is a fear that the production of HfB2 will be possibly terminated as a result of worldwide discussions for the environmental problems possibly caused upon producing the atomic fuel.
In addition to these problems, for the heat generating resistor composed of HfB2 used in ink jet heads, there are other problems such as will be described below.
Firstly, there is a new demand for the performance of the heat generation resistor used in an ink jet head. That is, in recent years, it has been discussed that as long as the heat generating resistor of an ink jet head is controllable in terms of the quantity of ink discharged, double pulsation for a pulse applied to the heat generating resistor is more effective in order to conduct color-printing by the ink jet head. In order to make it possible to conduct the double pulsation for a pulse applied to the heat generating resistor, the heat generating resistor is required to be markedly high particularly in terms of the durability. However, the heat generating resistor composed of HfB2 does not sufficiently meets this requirement.
Secondly, there is a problem in view of the production of a heat generating resistor composed of HfB2. That is, since a HfB2 film as the heat generating resistor is formed by means of the RF sputtering manner, the resulting HfB2 films are unavoidably varied in terms of their quality. Particularly, a Hf material used as the target is often accompanied by certain foreign matters and those foreign matters are liable to contaminate into a HfB2 film formed.
Incidentally, it is recognized that the foreign matters contained in the HfB2 film are liable to impart negative influences to semiconductor elements such as metal-oxide-semiconductors. In addition, such HfB2 film contaminated with the foreign matters is not sufficient in terms of compatibility with such semiconductor element when produced using the HfB2 film.
In recent years, there have been developed a substrate for an ink jet head integrally provided with a signal-input logic circuit and a Bi-CMOS integrated circuit constituting a heater driver. When the above HfB2 film contaminated with foreign matters is used as the heat generating resistor in this substrate for producing an ink jet head, the aforesaid poor compatibility of the HfB2 film with the semiconductor elements entails a serious problem in that the resulting ink jet head unavoidably becomes insufficient in terms of the quality.
The present inventors made extensive studies through experiments in order to eliminate the foregoing problems in the case of using HfB2 as the heat generating resistor in an ink jet head. Particularly, the present inventors made experimental studies aiming at finding out a relevant material suitable as the constituent for the heat generating resistor for an ink jet head, which is free of such a drawback as in the case of HfB2 in terms of the stable supply and which can be easily produced by a relatively simple film-forming process, while focusing on tantalum nitride materials which once had been deemed as being not suitable as the constituent material of the heat generating resistor in an ink jet head.
In the experimental studies, the present inventors prepared a plurality of heat generating resistors each comprising a tantalum nitride material selected from the group consisting the foregoing TaN single body, Ta2N single body, and mixtures of these described in the foregoing prior art, and prepared a plurality of ink jet head provided with an increased number of discharging outlets using these heat generating resistors. And each of the resultant ink jet heads obtained was subjected to printing continuously over a long period of time in a manner of applying a pre-pulse and then applying a main pulse at a given interval for discharging ink (this manner will be hereinafter referred to as double pulsating manner). As a result, no satisfactory printing could be conducted in any case. And it was found that any of the heat generating resistors does not perform so as to meet the requirements desired therefor.
And further experimental studies by the present inventors resulted in finding a new tantalum nitride material containing TaN0.8 (hereinafter referred to as TaN0.8-containing tantalum nitride material) which is clearly distinguished from any of the foregoing conventional TaN single body, Ta2N single body, and mixtures of these and which makes it possible to obtain a desirable heat generating resistor which is hardly varied in terms of the resistant value even upon continuously applying a relatively large quantity of electric power thereto over a long period of time and which enables to provide a highly reliable ink jet head which stably and continuously exhibits printing performance in a desirable state even when printing is carried out by driving the ink jet head in the double pulsating manner.
The present invention has been accomplished on this finding.
Hence, the principal object of the present invention is to eliminate the foregoing problems in relation to the conventional heat generating resistor for a liquid jet head and to provide an improved heat generating resistor comprised of a specific TaN0.8-containing tantalum nitride material which is hardly varied in terms of the resistant value even upon continuously applying a relatively large quantity of electric power thereto over a long period of time and which enables to obtain a highly reliable liquid jet head which stably and continuously exhibits excellent ink discharging performance to provide high quality prints even upon repeated use over a long period of time.
Another object of the present invention is to provide a substrate for a liquid jet head which is provided with an improved heat generating resistor comprised of a specific TaN0.8-containing tantalum nitride material, a liquid jet head provided with said substrate, and a liquid jet apparatus provided with said liquid jet head.
A further object of the present invention is to provide an improved heat generating resistor comprised of a specific TaN0.8-containing tantalum nitride material which enables to obtain a highly reliable liquid jet head which stably and continuously exhibits excellent liquid discharging performance to provide high quality prints even when printing is carried out repeatedly over a long period of time by driving the liquid jet heat in the double pulsating manner, a substrate for a liquid jet head provided with said improved heat generating resistor, a liquid jet head provided with said substrate, and a liquid jet apparatus provided with said liquid jet head.
A further object of the present invention is to provide an improved heat generating resistor comprised of a specific TaN0.8-containing tantalum nitride material which enables to obtain a highly reliable liquid jet head provided with an increased number of discharging outlets which stably and continuously exhibits excellent liquid discharging performance to provide high quality prints even when printing is carried out repeatedly over a long period of time by driving the liquid jet head in the double pulsating manner, a substrate for a liquid jet head provided with said improved heat generating resistor, a liquid jet head provided with an increased number of discharging outlets and which is provided with said substrate, and a liquid jet apparatus provided with said liquid jet head.
A further object of the present invention is to provide an improved heat generating resistor comprised of a specific TaN0.8-containing tantalum nitride material having an excellent compatibility with semiconductor elements such as input-signal logic circuit, Bi-CMOS integrated circuit, and the like disposed in a substrate for a liquid jet head, a substrate provided with said semiconductor elements for a liquid jet head and which is provided with said improved heat generating resistor, a liquid jet head provided with said substrate, and a liquid jet apparatus provided with said liquid jet head.
A further object of the present invention is to provide an improved heat generating resistor having a stacked structure with a layer comprised of a specific TaN0.8-containing tantalum nitride material as one of the constituent layers which is hardly varied in terms of the resistant value even upon continuously applying a relatively large quantity of electric power thereto over a long period of time and which enables to obtain a highly reliable liquid jet head which stably and continuously exhibits excellent liquid discharging performance to provide high quality prints even upon repeated use over a long period of time, a substrate for a liquid jet head which is provided with said improved heat generating resistor, a liquid jet head provided with said substrate, and a liquid jet apparatus provided with said liquid jet head.